Ken Molay, a web presentation expert, suggests the idea of “move and stop, move and stop” when delivering demos over the web. Specifically, he recommends using your mouse to deliberately move to a location and then stop and leave the mouse still while you offer a brief verbal description; then move and stop again.
This practice gives the audience sufficient time to follow the mouse movements, particularly if there is a delay or latency in the web session. It also provides the audience with a brief respite from an otherwise constantly moving mouse!
While Ken makes this suggestion with regards to Remote Demos, the same principle can certainly be applied to face-to-face sessions.
More on Ken and his thoughts can be found at http://www.wsuccess.com/.